Conventionally, positioners have been provided in control valves, where the valve opening of the control valve is controlled by the positioner. This positioner includes a calculating unit for calculating a deviation between a control valve opening setting value sent from a higher-level device and an actual opening value that is fed back from the control valve, to generate, as a control output, an electric signal in accordance with this deviation; an electro-pneumatic converting device for converting, into a pneumatic pressure signal, the control output generated by the calculating unit; and a pilot relay for amplifying the pneumatic pressure signal, converted by the electro-pneumatic converting device and outputting the result, as a pneumatic pressure signal, to an operating device for the control valve (See, for example, Japanese Unexamined Patent Application Publication S62-28118).
In this positioner, the pneumatic converting device and pilot relay each may be of a positive operating mode or a negative operating mode. That is, the positive operating mode is of an operating system of a nature wherein the greater the input, the greater the output will be, where, on the other hand, the negative operating mode is of an operating system having a nature wherein the greater the input, the smaller the output will be. Given this, the operating mode of the positioner itself depends on the forms of operation of the built-in electro-pneumatic converting device and pilot relay. That is, as illustrated in FIG. 12, if the modes of operation of the electro-pneumatic converting device and the pilot relay are identical, then the positioner will be of the positive operating mode, but if the modes of operation of the electro-pneumatic converting device and of the pilot relay are opposite from each other, then the mode of operation of the positioner will be the negative. Furthermore, the type of positioner to use, in terms of the type of operating mode, is determined by the operating mode of the control valve wherein the opening is controlled by the positioner.
Here if, for example, a change is produced so as to control a control valve of the opposite operating mode from the control valve that has been controlled until that point, or if there is a failure in a positioner that has controlled the control valve, making it necessary to replace suddenly with a spare positioner, where this spare positioner and control valve are of different operating modes, then the operating mode of the positioner is changed through changing the operating mode of the built-in electro-pneumatic converting device through changing the direction of the electric current supplied to a magnetic excitation coil (See, for example, Japanese Unexamined Patent Application Publication 11-118526). Additionally, if the pilot relay that is built into the positioner is a multimode pilot relay (of a type wherein it is possible to select the positive operating mode or the negative operating mode), then the operating mode of the positioner can be changed by selecting the opposite operating mode from that which had been used up to that point.
However, in a conventional positioner it is not possible to know easily the actual operating mode of the positioner. Because of this, if an operator is instructed to change the operating mode of a positioner but has forgotten to change the setting or makes an error in changing the setting, it may be set in the control valve without the error being discovered, and thus there is a risk that not only will the control of the opening not be performed correctly because the operating mode of the positioner does not match the operating mode of the control valve, but there is also the risk of producing a problem that causes a failure in the system wherein the flow of the fluid is controlled by the control valve.
The present invention was created in order to solve the problem as set forth above, and the object thereof is to provide a positioner wherein it is possible to discern easily the current operating mode of the positioner.